I purchased a leased car (great shape, low miles, certified and the preset stations were several Conservative radio stations) and found three or four gift cards between the driver seat and console towards the back. The dealer had missed it and I have missed it despite vacuuming the entire floor several times over the first year. There was no way to trace the owner so I ended up with about $100 in clothing store gift cards and a couple of restaurant gift cards.
Nice, a miniature buying spree.
I used to leave gift cards ($10-$20) in rental cars when I travelled. I figured if they did a decent job cleaning the vehicle they would find them.